The true incidence of aortic stenosis among the general population is unknown but aortic sclerosis, its precursor, has been estimated to affect about 25% of people over age 65, while an estimated 3% of the population over age 75 have severe aortic stenosis. Severe aortic stenosis, when accompanied by symptoms of angina, syncope, or heart failure, is associated with high mortality rates. Two-dimensional and Doppler echocardiography are cornerstone tools for the evaluation and monitoring of aortic stenosis. Echocardiography helps identify the patient at risk of death and guide timing of aortic valve replacement. Other important diagnostic tools include cardiac catheterization, treadmill stress testing, and dobutamine stress echocardiography, although their use is limited to specific patient populations. Aortic valve replacement carries a significant operative risk of approximately 4.0%. However, risk of operative mortality varies according to comorbidities and disease presentation. There are many risk models that guide estimation of the risk of operative mortality. Understanding operative risk is important in patient care and the selection of patients for aortic valve replacement.